Revision with unchanged content. The spin of the electron plays the vital role in building future electronic devices which manipulate this quantum property of the electron. This has the potential for making a new-age in fundamental physics and device applications. Also the interaction of light with the spin of electron provides the ability to control magnetism in different magnetic systems. We in this book study the photoinduced ferromagnetism in dilute magnetic semiconductors by constructing the famous BCS-wave function and BV-transformations applicable to these systems. The system of electrons, holes, magnetic impurities and incident light which is adequetly described by a quantum many-body hamiltonian undergoes a phase transition when temperature is lowered below the critical temperature which is determined by the parameters of the system. This book is addressed to theoretical physicists and researchers in condensed matter physics. It is also directed to the senior graduate students who want to learn the application of many-body theory to physical systems.